Question

What is the lowest unoccupied molecular orbital in F2?

Answer 1

σ*2pₓ, also called
`3\sigma_(u)\text{*}`

Explanation:

I have drawn the MO diagram for fluorine below.

Each F atom contributes seven valence electrons, so we fill the MOs of fluorine with 14 electrons.

We have filled the
`\pi \text{*2p}_(y)` and
`\pi \text{*2p}_(z)` MOs.

They are the highest occupied molecular orbitals (HOMOs).

The next unfilled level (the LUMO) is the σ*2pₓ orbital. If you use the symmetry notation, it is called the
`3\sigma_(u)\text{*}` orbital.

This is the orbital that fluorine uses when it acts as an electron acceptor.